rod, ros- to gnaw (robust, erosion, corrosive)
saga- perceive (sagacity, sagacious, presage)

rod/ros: to gnaw

Robust: (adjective) Not perturbed by or attending to subtleties or difficulties; uncompromising and forceful.
Sentence: My mother has a robust personality; she never caves on her decision of letting me borrow the car.

Erosion: (noun) The gradual destruction or diminution of something.
Sentence: The beach would get smaller after every storm because it was eroding.

Corrosive: (adjective) Harmful or destructive; deleterious.
Sentence: Acid can be corrosive to the skin and burn it.

Saga: Perceive

Sagacity: (noun) Quality of being discerning, sound in judgment, and farsighted.Having or showing good judgement.
Sentence: His most valuable personality trait is his sagacity.

Sagacious: (adjective) Having or showing keen mental discernment and good judgment; shrewd.
Sentence: The girl has a sagacious personality as her first opinion of someone is usually right.

Presage: (noun) An indication or warning of a future occurrence; an omen.
Sentence: When animals begin to move uphill it is a presage of a tsunami.